As the SW, you release the Emperor's spirit from the current voice, a Voss, as part of your class quest. Servant One mentions they would be making preparations for a new host for the Voice. That is what you kill at the end of the JK storyline. In Revan, it says the Emperor was once a member of the original Sith race, but became something entirely different, and has pure black eyes.

Spoiler

if you read the Revan novel, you will know that vitiate ( the emperors name), has black eyes since birth, and yes he was a sith pureblood. Not an Original sith mind you. The original sith they no longer exist, the Pureblood sith you see in game are hybrids of Sith and humans. But at this time they are the only genetic legacy from the sith thus for named purebloods, as they by genetic heritage are descendents of the original dark jedi and lords of the sith of old. Unless there is soem massassi still lying arround in yavin

Peace is a lie, there is only passion.
Also

Quote:

HK47: Statement: You are like a delightful random cruelty generator, master, poisoning all you touch with your presence. You are a testament to all organic meatbags everywhere.